The object of this project is to study the etiology and pathogenesis of mucosal diseases of the oral cavity, with the ultimate goal of treatment and prevention. At the present time, emphasis is on recurrent aphthous ulcers, Behcet's disease, and Sjogren's syndrome. Efforts are being made, by a variety of techniques, to demonstrate a viral etiology and to look for immunological abnormalities. Double-blind clinical trials are being carried out to determine the efficacy of various drugs.